The unique performance of polyimide compositions under stress and at high temperatures have made them useful in applications requiring high wear resistance, particularly at conditions of high pressure and velocity. Some examples of such applications are aircraft engine parts, aircraft wear pads, automatic transmission bushings and seal rings, tenter frame pads and bushings, material processing equipment parts, and pump bushings and seals.
Typically, a polyimide component in applications as described above is intended to function as a sacrificial, or consumable, component, thereby preventing or reducing the wear or damage that a more costly mating or adjacent component would experience if it were mated against some other component. However, as the polyimide component wears, the resulting increased clearances can result in other adverse effects, such as increased leakage (of air pressure or fluid) or increased noise, thereby reducing the operating effectiveness of the entire system in which the polyimide component is contained. Restoring the system to its original operating effectiveness would require replacement of the worn polyimide component with a new un-used polyimide component. Replacement may require disassembly, reassembly, testing and re-calibration (“service”) of the system, resulting in considerable costs in terms of down-time and labor. Thus, a polyimide component that demonstrates a lower rate of wear is desirable to reduce the frequency of replacement and service, thereby reducing cost.
Improvement in thermooxidative stability (“TOS”) as a consequence of end-capping has been found in polyimides containing flexible linkages [see, e.g., Meador et al., Macromolecules, 37 (2004), 1289-1296]. End-capping has actually been found to decrease TOS in certain rigid aromatic polyimide compositions, however. Despite the variety of polyimide compositions, and fillers for same, that have previously been available, and despite the previous work in the art, a need still remains for polyimide compositions that exhibit as molded parts the desirably high degree of wear resistance at the higher temperatures and increased pressure velocity load currently required for applications such aircraft engine parts, while maintaining the other advantageous attributes of the polyimide material.